See the link below. It includes a stack based scripting language (essentially a subset of Forth) for processing transactions so you can do some customization in how transactions unfold. As I understand it (and I don't know much about Ethereum) a big difference is that Eth has a Turing complete scripting language that can run code as part of transaction, while bitcoin only has a subset that doesn't include e.g. looping.

https://en.bitcoin.it/wiki/Script